1. Technical Field of the Invention
The present invention relates generally an image-transferring system which may be employed in an electrophotographic type of copying machine. More specifically, the invention relates to an improvement on an image-transferring system with a cleaner for cleaning a surface of a transfer roller which serves to transfer a toner image formed on a photosensitive medium onto a transfer paper.
2. Background Art
A conventional color printer will be described hereinbelow with reference to FIGS. 6-8.
A stack of sheets of transfer paper 37 is stored on a paper stacking plate 102 arranged in a paper tray 10 1 so that the transfer paper 37 may be transported to a pick-up roller 103. A one-cycle clutch 104 is arranged to restrict rotational movement of the pickup roller 103. A register sensor 105 is mounted above the pick-up roller 103 to detect the transfer paper 37 fed from the paper tray 101. On the transfer paper 37, a toner image is transferred by an image-transferring device, as will be described later, and then fixed thereon by a fixing unit 108 which includes a heat roller 106 for heating the transfer paper 37 and a pressure roller 107 for urging the transfer paper 37 against the heat roller 106. A first ejected paper sensor 109 is arranged to detect the image-transferred paper passed through the fixing unit 108. A pair of ejecting paper rollers 110 and 111 directs the image-transferred paper toward an outlet port. A second ejected paper sensor 112 is installed downstream of the ejecting paper rollers 110 and 111 to detect the image-transferred paper in the outlet port. A pair of outlet rollers 113 and 114 feeds the image-transferred paper to an ejected paper tray 115. A selector flap 116 is provided to select an ejecting path for the image-transferred paper. A selector roller assembly including three rollers 117 transports the image-transferred paper along the ejecting path selected by the selector flap 116. An exposure unit 118 is disposed in an upper portion of the printer, and serves to radiate exposing light onto a belt-like photosensitive medium 1 to form a latent image thereon. A controller 119 and a high-voltage unit 120 are provided.
FIG. 7 shows the image-transferring device when not serving to image-transfer. The belt-like photosensitive medium 1 is made of a dielectric material, and is supported for rotation at a constant speed for establishing a developing operation. Around the belt-like photosensitive medium 1, an electrifier 2 for electrifying the belt-like photosensitive medium 1, the exposure unit 118 (not shown in FIG. 7) for exposing the belt-like photosensitive medium 1, four developing units 4 for developing three primary colors and black on the belt-like photosensitive medium 1 respectively, a cleaner 5 for removing unnecessary toners left on the belt-like photosensitive medium 1, and a discharging unit 6 for removing a charge from the belt-like photosensitive medium 1. The belt-like photosensitive medium 1 contacts with an intermediate transfer belt 7 at a location downstream of the developing units 4 in a rotational direction of the belt-like photosensitive medium 1.
The intermediate transfer belt 7 is made of a dielectric material, and is driven to rotate in synchronism with the belt-like photosensitive medium 1. At a location upstream of a contact area of the intermediate transfer belt 7 with the belt-like photosensitive medium 1 in a rotational direction of the intermediate transfer belt 7, a cleaner 8 is arranged to remove unnecessary toners left on the intermediate transfer belt 7. The cleaner 8 is attached to one end of a pivotable plate 9 which is pivotably supported by a shaft 10. On the other end of the pivotable plate 9, a cam 11 and a spring 12 which serves to urge the pivotable plate 9 against the cam 11 are secured.
At a location downstream of the contact area of the intermediate transfer belt 7 with the belt-like photosensitive medium 1 in the rotational direction of the intermediate transfer belt 7, a platen or transfer roller 21 is arranged which is pivotally mounted on an end of a pivotable plate 23 functioning as a cam follower, and is driven to rotate in synchronism with the rotational movement of the intermediate transfer belt 7. The pivotable plate 23 is pivotally supported by a shaft 24. A spring 26 is installed on the other end of the pivotable plate 23 opposite the end on which the transfer roller 21 is arranged. The spring 26 serves to urge the pivotable plate 23 against a surface of the cam 25. The cam 25 is secured on a shaft 27 and includes a projecting portion 25a for separating the transfer roller 21 from the intermediate transfer belt 7 and a recessed, or fiat portion 25b for bringing the transfer roller 21 into engagement with the intermediate transfer belt 7. Attached to an end of the shaft 27 is a half cycle clutch 28.
The half cycle clutch 28 includes a pair of engaging portions 28a at locations substantially corresponding to the projecting portion 25a and the fiat portion 25b of the cam 25, respectively. One of the engaging portions 28a engages an actuator 29a to restrict rotational movement of the half cycle clutch 28. The actuator 29a is drawn to a solenoid 29 upon energization of the solenoid thereof so that it is shifted away from from the engaging portion 28. Alternatively, when the solenoid is deenergized, it will cause a spring 29b to bias the actuator 29a into engagement with the engaging portion 28 of the half cycle clutch 28.
A cleaning blade 31 is bonded to a cleaning frame 30. The cleaning blade 31 is operable to remove unnecessary toners and/or paper powders from a surface of the transfer roller 21. The cleaning frame 30 is installed on the pivotable plate 23 at a location where the cleaning blade 31 contacts the transfer roller 21. The transfer roller 21 and the cleaning blade 31 are urged into constant engagement with each other by their own elasticity.
Adjacent the intermediate transfer belt 7 and the transfer roller 21, a pair of feeding rollers 32 and 33 for feeding the transfer paper 37 to the image-transferring station and paper guide plates 34, 35, and 36 are arranged.
In operation, when an image-transferring command is issued to the printer, the controller 119 is initiated to prepare image-transferring data and transports the transfer paper 37 to the image-transferring station in the following manner. The one cycle clutch 104, as shown in FIG. 6, is initially actuated to cause the pick up roller 103 to rotate by one cycle so that one sheet of transfer paper 37 stacked on the paper stacking plate 102 is fed out of the paper tray 101. When the register sensor 105 detects the presence of the transfer paper 37 traveling along a feed path, it will cause the transport of the transfer paper 37 to be stopped so that the transfer paper 37 waits temporarily while being held by the feeding rollers 32 and 33 for synchronism with image-transferring timing.
A full color image of the image-transferring data is developed on the belt-like photosensitive medium 1 in the following manner. The belt-like photosensitive medium 1 which has already been cleaned by the cleaner 5 and discharged by the discharging unit 6, is electrified by the electrifier 2 again and then exposed to the exposure light 3 from the exposure unit 118 corresponding to one color of a transferring image to form a latent image thereon. When the belt-like photosensitive medium 1 passes through the developing unit 4, a toner corresponding to one color of the transferring image is deposited on the latent image formed on the medium 1 according to an image shade to form a one-color image. The toner is then transferred onto the intermediate transfer belt 7. The belt-like photosensitive medium 1 then proceeds to a subsequent developing process of developing another color. With repetition of the above process, the belt-like photosensitive medium transfers the toners of full color onto the intermediate transfer belt 7 in overlapping relation according to the shade of the transferring image.
During a time period from the beginning of the synthesis operation of the toners of four colors on the intermediate transfer belt 7 to the end of image-transferring operation onto the transfer paper, the cleaner 8 is maintained separate from the intermediate transfer belt 7 by the pivotable plate 9 urged by the cam 11 in a counterclockwise direction, as viewed in the drawings. The transfer roller 21 is also maintained separate from the intermediate transfer belt 7 by the pivotable plate 23 urged by the cam 25 downward until the synthesis operation on the intermediate transfer belt 7 is completed.
The image-transferring operation onto the transfer paper 37 will be described with reference to FIG. 8.
When the transfer paper 37 is transported by the feeding rollers 32 and 33 to the given location in the image-transferring station, the solenoid 29 is turned on and off one time, thereby causing the engaging portion 28a of the half cycle clutch 28 to be released for allowing rotation thereof. Upon rotation by half, the other engaging portion 28a engages the actuator 29a so that the movement of the half cycle clutch 28 is restricted. During the half revolution of the half cycle clutch 28, the cam 25 arranged coaxially with the clutch 28 also rotates by half, causing the pivotable plate 23 which is urged against the fiat portion 25b of the cam 25 by the spring 26 to rotate about the shaft 24 so that the transfer roller 21 engages the intermediate transfer belt 7. Immediately after this engagement, the transfer paper 37 is fed to the image-transferring station and then is held between the intermediate transfer belt 7 and the transfer roller 21 so that the full color toner image provided on the intermediate transfer belt 7 is transferred onto the transfer paper 37.
Subsequently, when the image-transferred paper 37 has passed through the image-transferring station, the solenoid is turned on and off again. The half cycle clutch 28 then repeats the above mentioned operation. The transfer roller 21 is shifted away from the intermediate transfer belt 7 and waits a subsequent image-transferring operation in the position, as shown in FIG. 7.
While the image-transferred paper 37 travels on the paper guide plate 36, the full color toner image is fixed by the fixing unit 108, as shown in Fig, 6. Upon the passage of the image-transferred paper 37 through the fixing unit 108 being detected by the first ejected paper sensor 109, determination is made which surface of the printed paper 37 should be placed upward on the ejected paper tray 115 and the selector flap then selects the ejecting path so that the image-transferred paper 37 is ejected by the ejected paper rollers 110 and 111 and the outlet rollers 113 and 114 onto the ejected paper tray 115 with the selected surface being placed upward. When the second ejected paper sensor 112 detects the presence of the image-transferred paper 37, all image-transferring operations terminate.
With the above arrangements, for a period of time between the transport of the transfer paper to the image-transferring station and the ejection thereof to the ejected paper tray 115, the image-transferring and the transfer paper transport mechanisms remain operating. The transfer roller 21 thus remains rotating together with the cleaning blade 31 which is urged into constant engagement with the transfer roller 21. Usually, the transfer roller 21 and the cleaning blade 31 are made of an elastic material such as urethane or silicone rubber. Therefore, the transfer roller 21 and the cleaning blade 31 tend to wear prematurely, resulting the lifespan of the system being shortened.